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The effects of restoration on the structure and function of litter invertebrate communities in New Zealand native forest remnants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Palmerston North, New Zealand

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Abstract

Much of New Zealand‘s remaining lowland forest exists as small, often degraded and
heavily disturbed remnants on private farmland. Disturbances, such as livestock
grazing and browsing by mammalian pests, are known to have a detrimental effect
on native vegetation of these remnants. However, it is unclear what impact these
disturbances have on the structure and function of forest floor invertebrate
communities. Existing studies of forest fragmentation have predominantly focused
on the effects of remnant area and shape, rather than remnant condition. This study
examines how litter invertebrate habitat, community structure, and leaf litter
decomposition, vary between grazed and ungrazed (fenced) remnants of differing
size, and nearby forest reserves. Secondly, I examine how invertebrate community
structure and function recover with time since livestock exclusion, with and without
additional mammalian pest control.
I found that grazed remnants provide dramatically altered habitat for litter
invertebrates, compared to fenced remnants and large forest reserves. Grazed
remnants are typified by having higher soil compaction, minimal understorey
vegetation, and reduced litter cover. Consequently, grazed remnants have
depauperate, yet highly variable invertebrate communities, compared to fenced
remnants and forest reserves. Even very small forest remnants can support litter
invertebrate communities very similar to that of larger forest reserves, provided they
are protected from livestock grazing. Furthermore, invertebrate communities show
strong recovery over time since livestock exclusion, particularly when livestock
exclusion is combined with mammalian pest control measures. I found that litter
decomposition rates did not differ between management treatments in my first
observational study. However, in the second observational study, leaf decomposition
rates at the edge of remnants increased with time since livestock exclusion,
suggesting that restoration actions can lead to changes in ecological functioning.
Small native forest remnants have high ecological value and substantial
restoration gains can be made through the relatively simple action of fencing to
exclude livestock.